1. Field of the Invention
The present invention relates to a key switch device suitable for use in a keyboard used as an input device of a personal computer, a word processor, or various other devices, and more particularly to a guide supporting mechanism for guiding and supporting a key top between a raised position and a lowered position.
2. Description of the Related Art
FIGS. 6 to 8 illustrate a conventional key switch device of the above-described type. The key switch device comprises a key top 41 molded from synthetic resin such as ABS resin; a holder member 52 disposed below the key top 41; a guide supporting member 44 for guiding and supporting the key top 41 between a raised position situated away from the holder member 52 and a lowered position situated close to the holder member 52; a switch member 57 mounted to the top surface of the holder member 52; and a rubber spring 58 disposed between the key top 41 and the switch member 57.
A character (not shown), such as a letter of the alphabet, is printed on the top surface of the key top 41. As shown in FIG. 6, rotary stopper sections 42 and sliding stopper sections 43 are integrally formed with the key top 41 so as to extend downward from the lower surface of the key top 41. A stopper hole 42a is formed in each rotary stopper section 42, while a stopper hole 43a is formed in each sliding stopper section 43.
The guide supporting member 44 comprises first and second link members 45 and 48 molded from synthetic resin material. As shown in FIG. 7, the first link member 45 is formed into a substantially U shape by a pair of arms 46 parallel to each other, and a connecting section 47 which integrally connects the pair of arms 46. A stopper pin 46a protrudes outward from one end of each arm 46, while a stopper pin 46b protrudes outward from the other end of each arm 46. A shaft hole 46c is formed in the center portion of each arm 46 so as to oppose each other.
The second link member 48 comprises a base section 49 including a circular hole 49a, and a pair of arms 50 formed consecutively at one end of the base section 49 so as to be parallel to each other. A stopper protrusion 50a protrudes from one end of each arm 50. A pair of outwardly protruding stopper pins 49b are formed on the opposite end of the base section 49. Outwardly protruding shafts 49c are provided on opposing ends of the base section 49.
As shown in FIG. 6, the first and second link members 45 and 48 are disposed so as to cross each other in an X-shaped configuration by positioning the base section 49 of the second link member 48 at the inner side of the pair of arms 46 of the first link member 45 and fitting the shafts 49c of the base section 49 into the corresponding shaft holes 46c in the arms 46. Crossing sections 51 formed by the shafts 49c and the shaft holes 46c allow the first and second link members 45 and 48 to rotate with respect to each other. The stopper protrusions 46b of the first link member 45 are slidably stopped in the corresponding stopper holes 43a in the key top 41, while the stopper pins 49b of the second link member 48 are rotatably stopped in the corresponding stopper holes 42a in the key top 41.
The holder member 52 is a metallic flat plate, and, as shown in FIG. 7, has a pair of slits 53a and 53b parallel to and opposing each other. When a flat-plate portion between the slits 53a and 53b is made to protrude thereabove from below, a sliding stopper section 54 including a stopper hole 54a is formed. In addition, two pairs of slits 55a and 55b are formed in the holder member 52 so as to be separated from the pair of slits 53a and 53b in a longitudinal direction thereof and so as to be parallel thereto. When a flat-plate portion between each pair of slits 55a and 55b is made to protrude thereabove from below, a rotary stopper section 56 including a stopper hole 56a is formed between its corresponding pair of slits 55a and 55b.
The stopper pins 46a of the first link member 45 are rotatably stopped by the stopper holes 56a in the corresponding rotary stopper sections 56, while the stopper protrusions 50a of the second link member 48 are slidably stopped by the stopper holes 54a in the sliding stopper section 54. The rotary stopper sections 56 at the holder member 52 are made to correspond with the sliding stopper sections 43 of the key top 41 by the first link member 45, while the sliding stopper section 54 of the holder 52 is made to correspond with the rotary stopper sections 42 at the key top 41 by the second link member 48.
The switch member 57 is formed by placing a top sheet, a spacer, and a bottom sheet upon each other in that order. The top sheet, spacer, and bottom sheet are not shown. Contact electrodes are formed on the bottom surface of the top sheet and the top surface of the bottom sheet, and are separated by a predetermined distance by the spacer so as to oppose each other. The bottom surface of the bottom sheet is brought into contact with the top surface of the holder member 52 in order to mount the switch member 57 to the holder member 52 with a suitable means, such as an adhesive.
The rubber spring 58 is formed of a rubber material and has a reversed conical shape. As shown in FIG. 6, it has an annular bottom section 58a which supports a top section 58c through a thin resilient wall 58b, and an actuating protrusion 58d formed on the lower surface of the top section 58c. The rubber spring 58 is disposed between the key top 41 and the switch member 57 by affixing the annular bottom section 58a to the top sheet of the switch member 57; is in contact with the bottom surface of the key top 41 as a result of inserting the top section 58c into the hole 49a in the second link member 48; and supports the top key 41 at a raised position situated away from the holder member 52 as a result of cooperating with the guide supporting member 44. The actuating protrusion 58d is opposed to the top surface of the top sheet in correspondence with the locations where the contact electrodes on the switch member 57 are formed.
In the key switch device having the above-described structure, when the operator presses the top surface of the key top 41, the key top 41 moves downward, causing the stopper protrusions 46b of the first link member 45 to slide in the stopper holes 43a in their corresponding stopper sections 43 in the direction of arrow G, and the stopper pins 49b of the second link member 48 to rotate in the stopper holes 42a in their corresponding rotary stopper sections 42. At the same time, the stopper pins 46a of the first link member 45 rotate in the stopper holes 56a in the rotary stopper sections 56, and the stopper protrusions 50a of the second link member 48 slide in the stopper holes 54a in the sliding stopper section 54 in the direction of arrow G.
This causes the first and second members 45 and 48 to be pushed downward as they rotate with the crossing sections 51 serving as a fulcrum, so that the key top 41 which is guided by the first and second link members 45 and 48 move downward along with the crossing sections 51. When the key top 41 moves downward, the rubber spring 58 is pushed downward by the key top 41, so that the resilient wall 58b is buckled, whereby a tactile feel is experienced. Immediately thereafter, as shown in FIG. 8, the key top 41 is positioned at a lowered position situated close to the holder member 52, and the actuating protrusion 58d presses and flexes the top sheet of the switch member 57. Therefore, the contact electrode on the top sheet comes into contact with the contact electrode on the lower sheet, thereby bringing these contact electrodes into electrical conduction, and turning on the switch device.
When, in this state, the pressing force on the top surface of the key top 41 is removed, the rubber spring 58 returns to its original reversed conical shape by the resilient force of the resilient wall 58b. Therefore, the key top 41 is pushed upward by the ascending top section 58c, the stopper protrusions 46b of the first link member 45 slide in the stopper holes 43a in the corresponding sliding stopper sections 43 in the direction of arrow H, and the stopper pins 49b of the second link member 48 rotate in the stopper holes 42a in the rotary stopper sections 42. At the same time, the stopper pins 46a of the first link member 45 rotate in the stopper holes 56a in the corresponding rotary stopper sections 56, and the stopper protrusions 50a of the second link member 48 slide in the stopper holes 54a in the stopper section 54 in the direction of arrow H.
This causes the first and second link members 45 and 48 to rotate with the crossing sections 51 as a fulcrum and rise upward, so that the key top 41 is guided by the first and second link members 45 and 48 and moves upward along with the crossing sections 51 to its original raised position. With the upward movement of the top section 58c, the top sheet of the switch member 57 flexed by the actuating protrusion 58c returns to its original shape due to its own flexibility, so that the contact electrode on the top sheet separates from the contact electrode on the bottom sheet, causing the contact electrodes to be brought out of electrical conduction, and, thus, the switch device to be switched off.
In the above-described conventional key switch device, the first link member 45 has portions with thicknesses X below the stopper protrusions 46b, and the second link member 48 has portions with thicknesses Y above the stopper protrusions 50a, so that the height of the conventional key switch device becomes larger by an amount corresponding to the thicknesses X and Y in a vertical direction. This in turn increases the thickness of the keyboard, itself, used in the key switch device. When an attempt is made to remove the portions of the first and second link members 45 and 48 with the thicknesses X and Y, and to reduce the size of the rubber spring 58 in a vertical direction in order to make the key switch device thinner by a corresponding amount, the first and second link members 45 and 48, which are molded from synthetic resin material, do not have sufficient rigidity, so that they get deformed and break due to the pressing force on the key top 41. Thus, the key top 41 cannot be smoothly guided and supported.